Pharmacodynamics – drug-receptor interactions

Pharmacodynamics – drug-receptor interactions

1. most drugs create their effects in the body by attaching to special sites called receptors on cells

2. when drug molecules attach to a receptor, they can stimulate the cell to act and are called agonists

3. by attaching to a receptor, drug molecules can prevent something else from attaching and causing an effect and are described as antagonists or blockers

   *Morphine competes with Narcan. When Morphine is locked on cells, Narcan can't lock on. narcotic antagonists. This is important for renal patients who can't excrete enough Morphine fast enough

4. a drug may latch onto a site to prevent a hormone or a neurotransmitter from attaching to the cell and turning on a function

5. if the drug is on, the other chemical cannot also be on the receptor

6. because there is competition for the receptor sites, the chemical that is present in the largest amount, either the drug or the internal regulator, is the most likely to be near an open receptor and attach to the receptor site

7. most drugs that are antagonists are competitive; only a very few are not

Pharmacodynamics – nonreceptor responses

Although most drug effects are related to drug-receptor responses, some drugs exert their effect by reacting physically or chemically with other molecules in the body. for example:

1. antacids react with HCL & raise pH (make stomach more alkaline)

2. heparin – anticoagulant physically thinning blood

Variables that Influence the Dose of a Drug – potency and efficacy

1. a certain level of a drug must be present in the body to produce an effect called the Minimum Effective Concentration (MEC)

2. the amount of a drug that must be given in order to produce a particular response – its relative pharmacologic activity is called the potency of a drug

3. two drugs may have different potencies but the same efficacy

4. rarely is potency the most important consideration when selecting a drug

Variables that Influence the Dose of a Drug – selecting a drug may depend on:

1. pill size

2. cost of each drug

3. the adverse effects from each one

4. route of administration

If drugs have similar potencies, but different efficacies, the drug that has better efficacy is usually preferred because this drug does a better job of achieving the desired therapeutic effect